Apparatus and methods for power management in integrated circuits

ABSTRACT

A programmable logic device (PLD) includes a non-volatile memory, a configuration memory, and a control circuitry. The control circuitry couples to the non-volatile memory and to the configuration memory. A set of voltages are derived from the outputs of the control circuitry, and are applied to circuitry within the PLD.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 11/316,390,filed on Dec. 22, 2005 now U.S. Pat. No. 7,405,589, titled ‘Apparatusand Methods for Power Management in Integrated Circuits,’ which is acontinuation-in-part of U.S. patent application Ser. No. 11/204,570,titled ‘Apparatus and Methods for Optimizing the Performance ofProgrammable Logic Devices,’ filed on Aug. 16, 2005 now U.S. Pat. No.7,400,167; and U.S. patent application Ser. No. 10/865,402, titled‘Apparatus and Methods for Adjusting Performance of IntegratedCircuits,’ filed on Jun. 10, 2004 now U.S. Pat. No. 7,129,745, which isa continuation-in-part of U.S. patent application Ser. No. 10/848,953,titled ‘Apparatus and Methods for Adjusting Performance of ProgrammableLogic Devices,’ filed on May 19, 2004 now U.S. Pat. No. 7,348,827. Theforegoing applications are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The inventive concepts relate generally to power management ofintegrated circuits (ICs). More particularly, the invention concernsmanaging power consumption or dissipation in programmable logic device(PLDs) by using user-configurable and die-specific controls orparameters.

BACKGROUND

Modern ICs, including PLDs, have undergone a high level of increase incomplexity. The increased complexity of the devices has resulted inimproved performance levels and increased flexibility. As a consequence,the end-user has enjoyed a level of performance.

On the other hand, the complexity and the sheer number of transistorshas resulted in increased power consumption in the device. The increasedpower consumption results in higher device operating temperature andelevated die power densities. Those factors have given rise tochallenges in device and system thermal management, reliabilityproblems, and the like. A need therefore exists for managing the powerconsumption or dissipation in ICs, such as PLDs.

SUMMARY

The disclosed novel concepts relate to apparatus and methods formanaging power consumption or dissipation of ICs, such as PLDs. In oneexemplary embodiment, a PLD includes a non-volatile memory (NVM), aconfiguration memory, and a control circuit. The control circuit iscoupled to the non-volatile memory and to the configuration memory. Aset of voltages are derived from outputs of the control circuit, and areapplied to circuitry within the PLD.

In another exemplary embodiment, a PLD includes a set of circuitsconfigured to allow measuring delay characteristics of circuitry withinthe PLD. Power consumption of the PLD is optimized by using a modelderived from the delay characteristics measured using the set ofcircuits.

In a further illustrative embodiment, a method of generating a set ofvalues used to manage power consumption of a PLD includes generating aset of points corresponding to process variations of the PLD. For eachpoint in the set of points, the method further includes determining aset of voltages to be applied to the programmable logic device at thatpoint in order to minimize power consumption of the programmable logicdevice.

In yet another illustrative embodiment, a method of managing powerconsumption of an IC includes assigning all regions in a set of circuitregions in a design of the IC as high speed regions. The method alsoincludes assigning selectively a subset of regions in the set of circuitregions as low speed regions, and reverting the assignment of the subsetof regions to high speed regions depending on whether a timingspecification is met.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings illustrate only exemplary embodiments of theinvention and therefore should not be considered or construed aslimiting its scope. Persons of ordinary skill in the art who have thebenefit of the description of the invention appreciate that thedisclosed inventive concepts lend themselves to other equally effectiveembodiments. In the drawings, the same numeral designators used in morethan one drawing denote the same, similar, or equivalent functionality,components, or blocks.

FIG. 1 shows a general block diagram of a PLD according to anillustrative embodiment of the invention.

FIG. 2 illustrates a floor-plan of a PLD according to an exemplaryembodiment of the invention.

FIG. 3 depicts a block diagram of a portion of programmable logiccircuitry in a PLD according to an exemplary embodiment of theinvention.

FIGS. 4-7 show simplified block diagrams of circuit arrangements used tomanage power dissipation according to an exemplary embodiment of theinvention.

FIG. 8 illustrates a simplified diagram of various software modules orblocks that PLD CAD software according to illustrative embodiments ofthe invention uses.

FIG. 9 depicts a flow diagram for a method of generating a model used toprogram non-volatile memory or storage according to an exemplaryembodiment of the invention.

FIGS. 10A-10D show graphs of various quantities as a function of circuitregion speeds in exemplary embodiments of the invention.

FIG. 11 illustrates a simplified flow diagram for a method according toan exemplary embodiment of the invention for assigning PLD regions.

FIGS. 12A-12B depict graphs of normalized delay that correspond to powerconsumption management techniques according to exemplary embodiments ofthe invention.

DETAILED DESCRIPTION

The inventive concepts contemplate apparatus and associated methods formanaging the power consumption of ICs, including PLDs. The inventivetechniques use a combination of end-user configurable and die-specificparameters or controls in order to manage the power consumption ordissipation.

FIG. 1 shows a general block diagram of a PLD 103 according to anillustrative embodiment of the invention. PLD 103 includes configurationcircuitry 130, configuration memory (CRAM) 133, control circuitry 136,programmable logic 106, programmable interconnect 109, and I/O circuitry112. In addition, PLD 103 may include test/debug circuitry 115, one ormore processors 118, one or more communication circuitry 121, one ormore memories 124, one or more controllers 127, as desired. PLD 103further includes initialization circuitry 139 and non-volatile memory orstorage (NVM) 142, as described below in detail.

Note that FIG. 1 shows a simplified block diagram of PLD 103. Thus, PLD103 may include other blocks and circuitry, as persons of ordinary skillin the art understand. Examples of such circuitry include clockgeneration and distribution circuits, redundancy circuits, and the like.Furthermore, PLD 103 may include, analog circuitry, other digitalcircuitry, and/or mixed-mode circuitry, as desired.

Programmable logic 106 includes blocks of configurable or programmablelogic circuitry, such as look-up tables (LUTs), product-term logic,multiplexers (MUXs), logic gates, registers, memory, and the like.Programmable interconnect 109 couples to programmable logic 106 andprovides configurable interconnects (coupling mechanisms) betweenvarious blocks within programmable logic 106 and other circuitry withinor outside PLD 103.

Control circuitry 136 controls various operations within PLD 103,including aspects of the inventive concepts. Under the supervision ofcontrol circuitry 136, PLD configuration circuitry 130 usesconfiguration data (which it obtains from an external source, such as astorage device, a host, etc.) to program or configure the functionalityof PLD 103. Configuration data are typically used to store informationin CRAM 133. The contents of CRAM 133 determine the functionality ofvarious blocks of PLD 103, such as programmable logic 106 andprogrammable interconnect 109.

I/O circuitry 112 may constitute a wide variety of I/O devices orcircuits, as persons of ordinary skill in the art who have the benefitof the description of the invention understand. I/O circuitry 112 maycouple to various parts of PLD 103, for example, programmable logic 106and programmable interconnect 109. I/O circuitry 112 provides amechanism and circuitry for various blocks within PLD 103 to communicatewith external circuitry or devices.

Test/debug circuitry 115 facilitates the testing and troubleshooting ofvarious blocks and circuits within PLD 103. Test/debug circuitry 115 mayinclude a variety of blocks or circuits known to persons of ordinaryskill in the art who have the benefit of the description of theinvention. For example, test/debug circuitry 115 may include circuitsfor performing tests after PLD 103 powers up or resets, as desired.Test/debug circuitry 115 may also include coding and parity circuits, asdesired.

PLD 103 may include one or more processors 118. Processor 118 may coupleto other blocks and circuits within PLD 103. Processor 118 may receivedata and information from circuits within or external to PLD 103 andprocess the information in a wide variety of ways, as persons skilled inthe art with the benefit of the description of the invention appreciate.One or more of processor(s) 118 may constitute a digital signalprocessor (DSP). DSPs allow performing a wide variety of signalprocessing tasks, such as compression, decompression, audio processing,video processing, filtering, and the like, as desired.

PLD 103 may also include one or more communication circuits 121.Communication circuit(s) 121 may facilitate data and informationexchange between various circuits within PLD 103 and circuits externalto PLD 103, as persons of ordinary skill in the art who have the benefitof the description of the invention understand.

PLD 103 may further include one or more memories 124 and one or morecontroller(s) 127. Memory 124 allows the storage of various data andinformation (such as user-data, intermediate results, calculationresults, etc.) within PLD 103. Memory 124 may have a granular or blockform, as desired. Controller 127 allows interfacing to, and controllingthe operation and various functions of circuitry outside the PLD. Forexample, controller 127 may constitute a memory controller thatinterfaces to and controls an external synchronous dynamic random accessmemory (SDRAM), as desired.

FIG. 2 shows a floor-plan of a PLD 103 according to an exemplaryembodiment of the invention. PLD 103 includes programmable logic 106arranged as a two-dimensional array. Programmable interconnect 109,arranged as horizontal interconnect and vertical interconnect, couplesthe blocks of programmable logic 106 to one another. One may adjust thepower supply voltage and/or body bias of the transistors and variousblocks or regions in PLD 103 (either by applying different body biasvalues over time, or applying a set of body bias values to a subset orall of regions, blocks, etc.), as described below in detail.

In illustrative embodiments, PLDs according to the invention have ahierarchical architecture. In other words, each block of programmablelogic 106 may in turn include smaller or more granular programmablelogic blocks or circuits. For example, in one embodiment, programmablelogic 106 may constitute blocks of configurable logic named logic arrayblock (LAB), and each LAB may include logic elements (LEs) or othercircuitry, as desired. Persons of ordinary skill in the art who have thebenefit of the description of the invention understand, however, that awide variety of other arrangements, with varying terminology andtopology, are possible, and fall within the scope of the inventiveconcepts.

FIG. 3 shows a block diagram of programmable logic 106 in a PLDaccording to an exemplary embodiment of the invention. Programmablelogic 106 includes logic elements or programmable logic circuits 150,local interconnect 253, interface circuit 156, and interface circuit159. Logic elements 150 provide configurable or programmable logicfunctions, for example, LUTs, registers, product-term logic, etc., aspersons of ordinary skill in the art who have the benefit of thedescription of the invention understand. Local interconnect 153 providesa configurable or programmable mechanism for logic elements 150 tocouple to one another or to programmable interconnect 109 (sometimescalled “global interconnect”), as desired.

Interface circuit 156 and interface circuit 159 provide a configurableor programmable way for programmable logic 106 block of circuitry tocouple to programmable interconnect 109 (and hence to other programmablelogic 106, as FIG. 3 shows). Interface circuit 156 and interface circuit159 may include MUXs, registers, buffers, drivers, and the like, aspersons of ordinary skill in the art who have the benefit of thedescription of the invention understand.

In exemplary embodiments according to the invention, PLD 103 usesseveral voltages to supply power and body bias to various regions orcircuitry within PLD 103. More specifically, the inventive techniquesmanage power consumption by using some amount of NVM 142 and CRAM 133 onPLD 103. NVM 142 may store die-specific process-related information, andmay controls the values of various voltages, such as body bias voltagesor power supply voltages. The particular values of the voltages appliedto various regions or circuits may be derived using a combination ofinformation from CRAM 133 and NVM 142 (PLD computer-aided design (CAD)software flow, described below in detail, determines the values to storein CRAM 133).

The values stored in NVM 142 may be determined and programmed before useby the end-user, such as during test time of PLD 103. In this manner,PLD 103 stores values that minimize, manage, or optimize powerconsumption or dissipation for that particular die, according to one ormore configurations that are determined by CRAM 133. PLD CAD softwareflows facilitate that operation, and are used to assign appropriatevoltages to regions or circuits of PLD 103.

FIG. 4 shows a simplified block diagram of a circuit arrangement used tomanage power dissipation according to an exemplary embodiment of theinvention. The circuit arrangement includes CRAM 133, NVM 142, controlcircuitry 136, one or more regulators 168, and a desired number ofoptional I/O pads 165. Note that the circuit arrangement may use asubset (rather than all) of the information stored in CRAM 133 and NVM142.

Furthermore, as noted above, control circuitry 136 may perform a varietyof functions. Accordingly, block 136 in the figure may constitute a partof the circuitry and/or functionality of control circuitry 136 in FIG.1, as desired, and as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. One mayimplement NVM 142 in a variety of ways, as desired, and as persons ofordinary skill in the art who have the benefit of the description of theinvention understand. For example, one may use fuses, flash memory, andthe like.

Control circuitry 136 includes logic circuitry that receives its inputsfrom CRAM 133 and NVM 142, and provides a set of outputs to regulator(s)168. Regulator(s) 168 use the information provided by control circuitry136 to generate voltages that affect the speed or delay of the chip. Aspersons of ordinary skill in the art who have the benefit of thedescription of the invention understand, regulator(s) 168 may resideeither on-chip or off-chip, as desired. The choice of implementationdepends on a number of factors, such as design and performancespecifications, as persons of ordinary skill in the art who have thebenefit of the description of the invention appreciate.

Furthermore, additional logic circuitry or I/O pads 165 may be used toprovide communicate between the voltage selection circuitry in controlcircuitry 136 and voltage regulator(s) 168, as desired. Examples mayinclude interfaces that communicate using standard or other protocols,for instance to send encoded voltage value(s) to external voltageregulator(s), as desired. Other variations fall within knowledge ofpersons of ordinary skill in the art who have the benefit of thedescription of the invention.

In the example shown, the voltages are V_(DDL), V_(BBP), V_(BBN) _(—)_(LS), and V_(BBN) _(—) _(HS) Note, however, that one may generate anyappropriate or desired number of supply and/or body bias voltages, asdesired, and as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. Note that onemay apply different body bias voltages over time, as desired. Also, onemay apply a set of body bias values, for example, one body bias value toa portion or all of a region or set of regions, circuits, or blocks, andanother body bias value to a portion or all of a region or set ofregions, blocks, or circuits, and so on, as desired.

Voltage V_(DDL) is used to generate or provide the supply voltage,V_(DD), for some circuits on the chip. Note that, rather than generatingone supply voltage, regulator(s) 168 may generate any desired number ofsupply voltages. One may then use an appropriate set of supply voltages(or supply voltage) to provide power to a given circuit or block in PLD103, so as to manage its power consumption (and speed of operation).

Voltages V_(BBP), V_(BBN) _(—) _(LS), and V_(BBN) _(—) _(HS) constitutebody bias voltages applied to desired circuits, devices, or blockswithin PLD 103. In the example shown, voltage V_(BBP) is used for theN-well bias of some or all of the PLD's PMOS transistors. Further,voltages V_(BBN) _(—) _(LS) and V_(BBN) _(—) _(HS) are used for theP-well bias of some or all of the PLD's NMOS transistors.

Various regions, devices, or circuits on the chip may configurablyselect between the V_(BBN) _(—) _(LS) and V_(BBN) _(—) _(HS) voltages.Such voltages may be used as configurable body bias voltages, for use,for example, as described in U.S. patent application Ser. No.10/865,402, titled “Apparatus and Methods for Adjusting Performance ofIntegrated circuit,” filed on Jun. 10, 2004. Using V_(BBN) _(—) _(LS)results in relatively low speed (LS) operation (but with relativelylower power consumption), while using V_(BBN) _(—) _(HS) results inrelatively high speed (HS) operation (but with relatively higher powerconsumption). The choice of the body bias voltage depends on variousfactors, such as desired performance, desired power consumption, or atrade-off between the two, as persons of ordinary skill in the art whohave the benefit of the description of the invention understand.

One may optionally use I/O pads 165 or test pads that couple to controlcircuitry 136. I/O pads 165 may be used to force one or more of thevoltages to specific or desired values during testing of the PLD's die.In addition, or instead, one may use combining functions that considerthe information received from CRAM 133, NVM 142, and I/O pads 165 indetermining the voltages provided by various parts of PLD 103. Forexample, I/O pads 165 may be used to select between one of multiplevoltages provided to PLD 103 to dynamically adjust the voltages, asdesired.

Initialization circuitry 139 (not shown explicitly, but shown in FIG. 1)may also be used to power up PLD 103 in a known mode, with acorresponding level of voltages and, hence, power consumption. Some ofprogrammable logic 106 may also be used as part of control circuitry136, as desired. For example, part of the circuit that receives andprocesses information from I/O pads 165 may be implemented usingprogrammable logic 106. In addition, one may use a wide variety of otherarrangements, as persons of ordinary skill in the art who have thebenefit of the description of the invention understand.

FIG. 5 shows a simplified block diagram of a circuit arrangement used tomanage power dissipation according to another exemplary embodiment ofthe invention. The circuit arrangement includes NVM 142A-142C, MUX 175,CRAM 133, and regulator(s) 168. The NVM is structured, at least in part,as a set of NVM cells or elements 142A-142C. NVM elements 142A-142Crepresent settings or values that determine the corresponding voltagesfor a particular configuration. In the example shown, a voltage settingfor each of the supply voltage(s) and body bias voltage(s) is chosenbased on the desired or intended usage of PLD 103.

In the embodiment shown, MUX 175 selects a particular set of NVM cellsor values, depending on the contents of CRAM 133. More specifically,CRAM 133 provides selection signal(s) to MUX 175 which, in response,selects desired values as represented and provided by NVM elements142A-142C.

This aspect of the invention may be used to provide for optimal powersettings in a variety of specific configurations. For example, a PLD maybe used in one of multiple speed grades, say, grades 3 and 4. A givendie, however, may be sold as either a grade 3 or grade 4 die, providedthat it meets the specifications of the corresponding speed grade. NVM142 may store the voltage settings that optimize power while meetingtiming specifications in NVM elements 142A-142C. Thus, each of NVMelements 142A-142C may store values that correspond to appropriatevoltage levels for each desired or possible grade.

In another embodiment, NVM 142 may provide separate settings or valuesbased on the optimal speed balance between high speed and low speed PLDregions. A particular user's circuit may have its power optimized usinga specific speed for the low speed regions (and/or high speed regions).In this embodiment, a number of distinct speed settings for the highspeed and low speed regions are encoded in NVM 142. PLD CAD software canchoose among the settings that optimize power for a given design orperformance target or specification.

As one example, it might be desirable to set V_(BBN) _(—) _(HS) to meetthe timing specifications for a particular speed grade, but to adjustV_(BBN) _(—) _(LS) to a specific value that makes the speed of the lowspeed regions 10% or 20% (or other desired values) slower than the highspeed regions. Some NVM elements (say, 142A and 142B) would encodevalues that cause provision of appropriate voltages that result in thespecific speeds to be met by the low speed regions. The PLD CAD softwarecan then choose between a 10% and 20% (or other desired values) slowdown for the low speed region, and determine which setting minimizes orreduces power consumption.

In another embodiment, multiple speed settings beyond the speed gradesprovided may be encoded in CRAM 133. As one example, extra CRAM cells orelements may encode a slow down of 5%, 10%, 15% or 20% (or other desiredvalues) beyond the speed grade of the device. Using this technique, onemay optimize or manage power consumption of PLD 103 in a flexiblemanner.

Other exemplary embodiments, in which the data inputs to MUX 175 areCRAM cells or elements, and NVM 142 selects from among the variousvalues represented by CRAM elements, are also possible, as desired. FIG.6 illustrates such an embodiment. An appropriate number of cells orelements of NVM 142 would encode aspects of the process variation, andthe CRAM cells or elements 133A-133C would encode values that correspondto the voltages to be used at that particular point in the processvariation. Put another way, in such embodiments, the roles of CRAMelements and NVM elements are switched (compared to the embodiment inFIG. 5).

In other embodiments, one may partition the control and generation ofdesired voltages. FIG. 7 shows an exemplary embodiment that uses thistechnique. In the example shown, NVM elements encode valuescorresponding to body bias voltages for the corresponding speed gradeand relative speed of the high speed and low speed regions. CRAM 133separately encodes values used to produce the supply voltage(s) thatproduce an additional slow down compared to the nominal value of thespeed grade.

More specifically, CRAM 133 provides values to regulator 168A that usethose values to generate one or more supply voltages (or generatevoltages used to generate appropriate or desired supply voltages). Othercells or elements of CRAM 133 act as select signals so as to providevalues encoded in NVM cells or elements 142A-142C as outputs of MUX 175.In other embodiments, one may reverse the roles of CRAM 133 and NVM 142,as desired (see FIG. 6).

Using the various embodiments, one may provide a mechanism to manage PLDpower consumption while meeting the user's speed or timing constraints.Note that one may use I/O pads 165 to provide additional types ofcontrol or to take into account other parameters, as desired.

Generally speaking, one may use appropriately determined values of bodybias voltages in order to optimize the power consumption of the PLDcircuitry while meeting delay or speed specifications. Such body biasvoltages can minimize power consumption while meeting specific ordesired values of timing. One may use I/O pads 165 (see FIG. 4) to applyvarious voltages or patterns to the control circuit. The circuit isconfigured to a known state, and as each voltage pattern is applied, thepower consumption and delay of the circuit is measured.

In the case of a PLD, the known state of the PLD should reflect theusage of the PLD for which one desires to minimize power consumption,and may represent a typical or worst case user circuit, as desired. Aspecific voltage combination may be selected which minimizes powerconsumption, and NVM 142 is programmed to encode this combination. Thissequence may be repeated multiple times to provide the NVM settings foreach of the CRAM-addressable settings.

In another embodiment, on-chip circuits or test circuits (possiblyincluding specific test circuits) are provided to measure delay andpossibly power consumption. This approach may avoid measuring total diepower consumption during testing. For example, a set of test circuitsmay be provided that allow effective measurement of process variation ata single voltage or several voltages can be used. Such circuits mayinclude logic circuits of various P-type to N-type transistor widthratios, various transistor lengths and widths, and transistors withvarious threshold voltages and layout structures.

A relatively small number of test voltage patterns can be designed andused such that measuring the delay of the test structures at arelatively limited number of voltage levels can provide sufficientinformation about the process point in order to determine the optimalvoltages. As one example, one might provide a chain of inverters (say, 4inverters) with all combinations of P-type to N-type transistor widthratios of 4/1 and 1/1, and lengths of 0.1 micron and 0.2 micron. Theparticular circuits are chosen to provide an ability to measure thedifference in P-type and N-type transistor behavior, and lengthvariation, with a reasonable degree of independence in the measurements.

In general, one may advantageously use a set of test circuits thatmeasure aspects of device performance in a variety of ways, with atradeoff between the number of measurements and the optimality ofmanaging the power consumption. In a PLD, programmable logic 106 andprogrammable interconnect 109 may be used for some or all of the testcircuits, as desired.

The test measurements might be performed at various body bias voltagesfor each circuit arrangement (e.g., inverter chain). By performing astatistical analysis on the correlation of the measurements so obtainedto the optimal voltages, a model to predict the values encoded in NVM142 may be used. For example, one might measure the delay of inverterchain 1 at V_(BBN)=−0.3V, V_(BBP)=0.5V, and inverter chain 2 atV_(BBN)=0V, V_(BBP)=0.8V, etc. The delay of a given chain might bemeasured at more than one value of body bias and/or supply voltages, asdesired. The determination of a suitable set of measurements may be madeby choosing a set of measurements that span the range of electricalproperties and control voltage settings that affect performance andpower consumption, evaluating their effectiveness, and modifying the setof values as desired until satisfactory, desired, or acceptable resultsare achieved. Persons of ordinary skill in the art who have the benefitof the description of the invention understand that, in the presence ofnoise in the case of including on-die variation, a set of measurementsshould be constructed to be as orthogonal as possible, so that theunderlying variables can be determined with as small amount of error aspractical.

As noted, various aspects of the inventive concepts relate to methodsused or included in connection with PLD CAD software. FIG. 8 illustratesa simplified diagram of various software modules or blocks that PLD CADsoftware according to illustrative embodiments of the invention uses.They include design-entry module 503, synthesis module 506,place-and-route module 509, and verification module 512. The followingdescription provides a simplified explanation of the operation of eachmodule, followed by a description of methods relating to various aspectsof power management according to the invention.

Design-entry module 503 allows the editing of various design descriptionfiles using graphical or textual descriptions of a circuit or itsbehavior, such as schematics, hardware description languages (HDL), orwaveforms, as desired. The user may generate the design files by usingdesign-entry module 503 or by using a variety of electronic designautomation (EDA) or CAD tools (such as industry-standard EDA tools), asdesired. The user may enter the design in a graphic format, awaveform-based format, a schematic format, in a text or binary format,or as a combination of those formats, as desired.

Synthesis module 506 accepts the output of design-entry module 503.Based on the user-provided design, synthesis module 506 generatesappropriate logic circuitry that realizes the user-provided design. Oneor more PLDs (not shown explicitly) implement the synthesized overalldesign or system. Synthesis module 506 may also generate any glue logicthat allows integration and proper operation and interfacing of variousmodules in the user's designs. For example, synthesis module 506provides appropriate hardware so that an output of one block properlyinterfaces with an input of another block. Synthesis module 506 mayprovide appropriate hardware so as to meet the specifications of each ofthe modules in the overall design or system.

Furthermore, synthesis module 506 may include algorithms and routinesfor optimizing the synthesized design. Through optimization, synthesismodule 506 seeks to more efficiently use the resources of the one ormore PLDs that implement the overall design or system. Synthesis module506 provides its output to place-and-route module 509.

Place-and-route module 509 uses the designer's timing specifications toperform optimal logic mapping and placement. The logic mapping andplacement determine the use of routing resources within the PLD(s). Inother words, by use of particular programmable interconnects with thePLD(s) for certain parts of the design, place-and-route module 509 helpsoptimize the performance of the overall design or system. By proper useof PLD routing resources, place-and-route module 509 helps to meet thecritical timing paths of the overall design or system.

Place-and-route module 509 optimizes the critical timing paths to helpprovide timing closure faster in a manner known to persons of ordinaryskill in the art with the benefit of the description of the invention.As a result, the overall design or system can achieve faster performance(i.e., operate at a higher clock rate or have higher throughput).Place-and-route module 509 may use information about critical pathswithin the design or system to adjust power consumption of parts or allof the design or system, as desired.

Verification module 512 performs simulation and verification of thedesign. The simulation and verification seek in part to verify that thedesign complies with the user's prescribed specifications. Thesimulation and verification also aim at detecting and correcting anydesign problems before prototyping the design. Thus, verification module512 helps the user to reduce the overall cost and time-to-market of theoverall design or system.

Verification module 512 may support and perform a variety ofverification and simulation options, as desired. The options may includefunctional verification, test-bench generation, static timing analysis,timing simulation, hardware/software simulation, in-system verification,board-level timing analysis, signal integrity analysis andelectro-magnetic compatibility (EMC), formal netlist verification, andpower-consumption estimation, as desired. Note that one may performother or additional verification techniques as desired and as persons ofordinary skill in the art who have the benefit of the description of theinvention understand. Verification of the design may also be performedat other phases in the flow, as appropriate, and as desired.

One aspect of the inventive concepts relates to methods of generating amodel for programming or encoding the values in NVM 142, given aspecific set of measurements. FIG. 9 shows a flow diagram of a method ofaccomplishing that task. At 603, a set of values representing a possibleprocess variation is generated. Subsequently, in a loop (using a loopcounter, N, initialized at 606), each process point is evaluated twice.

The first evaluation, at 609, includes simulating (using a simulatorsuch as SPICE, well known to persons of ordinary skill in the art) theelectrical measurements that will be made of the test circuits. Thesecond evaluation determines, either by exhaustive simulations or acombination of simulations and analytical modeling, the optimal voltagesto be applied to the PLD for the specific process point. Using asimulation based approach, each test circuit is simulated at theproposed measurement condition to determine the measurement value (powerconsumption or delay, as appropriate). Using an analytical model basedapproach, each test circuit has its measurement predicted using apreviously generated model that predicts the measurement values at anygiven process variation.

At 615, the loop counter is incremented, and at 618 a determination ismade whether the loop should exit or continue (i.e., whether anyadditional process points remain). After completion of the loop, at 621,the set of data giving the measurements and optimal voltages are used asinput to generate a model giving the voltages as a function of themeasurements.

That task may be accomplished by any number of model optimizations, suchas generating a linear model or polynomial of some order that minimizesthe prediction error. A typical method would be to generate a leastsquares fit to a polynomial of some predetermined order, although onemay use other techniques, as persons of ordinary skill in the art whohave the benefit of the description of the invention understand. Ingeneral, any mathematical formulation that uses the values of themeasured test circuits as independent variables and fits the optimalvoltages to these variables can be used as a model, as desired.

At 624, an output for the method is generated. The output is the model,for example, an equation, such that taking the specified set ofmeasurements on the die may be input to the model to produce thespecific values to be programmed or encoded into NVM 142.

Note that, instead of simulating the die, it is possible to directlymeasure the power consumption and delay of a set of dies. Doing soentails total die power consumption measurements, which might be complexand time consuming, and not practical in production. One may thereforeopt for die measurement on a relatively limited number of dies togenerate the model, as desired. Programming NVM 142 in a productionenvironment would use the limited number of test measurements and thepreviously generated model.

Note that the above method assumes that the optimal voltage settings areknown for each process variation on a particular die. One normally wouldgenerate that information before the model generation described abovetakes place. A model, providing optimal voltage settings as a functionof process variation, may be generated by modeling a set of possibleprocess variations. At each process variation, a speed/power consumptionmeasurement is made across various voltage settings. The measurement maybe made either by simulation or measurement of an actual die, asdesired.

The number of high speed (HS) and low speed (LS) regions can bedetermined as a function of the speed of LS regions using a method suchas described below. FIG. 10A shows a graph of the fraction, F, of PLDregions that constitute LS regions. The fraction is shown as a functionof R, the ratio of the delay of LS regions to the delay of HS regions.At the left edge of the plot (i.e., R=1), the LS region delay is thesame as the HS region delay, so all regions can be LS. As the delay ofthe LS region increases, however, not as many regions can be convertedto LS (as described below) without violating timing constraints.

The power consumption for an optimal voltage setting that achieves adelay of HS region that is sufficient to meet timing, and an LS regionthat is some given amount slower than an HS region can be determined bysimulation or measurement. FIG. 10B shows a graph of the powerconsumption of LS regions as a function of the ratio R. One may combinetwo values, fraction of regions that are LS regions, and the powerconsumption of LS regions to determine overall power consumption as afunction of the ratio R. FIG. 10C shows a plot of total power.

One may repeat this process across each of the process variationsdescribed above. Doing so generates a number of curves for total powerconsumption. FIG. 10D shows a plot of a family of total powerconsumption curves generates using this technique. Each curvecorresponds to a particular possible process variation. One may thenselect a low speed region delay that minimizes power consumption. Thepower consumption may constitute worst case power consumption, averagepower consumption, or may be according to some other metric, as desired.The example shown in FIG. 10D illustrates the LS region delay thatminimizes the worst case power, P_(C), across all of the processvariations encountered.

One aspect of the invention relates to techniques for programming orencoding NVM 142 on each PLD as it is tested in order to optimize powerconsumption for that. In one embodiment, the PLD is configuredsequentially in a number of configurations. The configurations mayrepresent various mixes of HS and LS circuits or blocks in programmablelogic 106 (e.g., LABs) and provide circuits that allow the delay of theHS and LS blocks to be measured. For example, one configuration mayrepresent a proportion of 10% high speed LABs and 90% low speed LABs,and the constraint that the low speed LABs are no more than 10% slowerthan the high speed LABs. Another configuration might be 20% high speedLABs and 80% low speed LABs, and allow 15% slow down for the low speedLABs.

The total power consumption of the die is also measured. Combinations ofthe voltages (supply and body bias) will be applied and the powerconsumption and delay are measured at each voltage combination. At theend of the process, the set of voltages correspond to the lowest powerconsumption, such that the timing specifications are met, can beselected. One may then program or encode the corresponding values intoNVM 142. Note that multiple timing specifications or constraints mayexist and are accommodated, according to the speed grade beingevaluated. For example a particular PLD configuration might have atiming specification of 100 ns for speed grade 3 and 120 ns for speedgrade 4.

A variety of other embodiments of the inventive concepts are alsopossible that allow differing levels of complexity, as persons ofordinary skill in the art who have the benefit of the description of theinvention understand. As an example, in one embodiment, one may avoidmeasurement of power consumption, and reduce the number of voltagesettings by using test circuitry, as described above. After performingmodel generation once for the process, each chip has a specific set ofvoltages (supply and body bias) applied and each test circuit ismeasured at specific voltages. One may then use the model describedabove to compute the optimal voltages and program or encode them in NVM142.

As noted above, one aspect of the inventive concepts relates to methodsof configuring an PLD to minimize power consumption by usingconfigurable speed regions (configurable assignment of LS and HSregions, and determining which regions should be LS regions, and whichHS regions). The inventive concepts contemplate high speed and low speedregion assignment techniques, which assign specific speed designationsto configurable speed regions of PLD 103. The speed adjustment may beperformed using body bias voltage assignment, but is not so limited inscope, as persons of ordinary skill in the art who have the benefit ofthe description of the invention understand. Generally, one may use anyconfigurable apparatus or techniques for adjusting the speed and powerconsumption of region of PLD 103, as desired.

Note that the logic regions may be of any size and level of granularity.For example, they may constitute LEs, LABs, groups of LABs, etc., asdesired. As another example, they may constitute all of the LEs in asingle LAB, or all of the interconnect in a LAB, as desired. Many othervariations and combinations exist, as persons of ordinary skill in theart who have the benefit of the description of the invention understand.

Generally speaking, the assignment operates as follows: The design isplaced, routed, and timing analyzed as usual, assuming that all regionsconstitute high speed regions. Thereafter, each region is inspected andtentatively assigned a low speed region designation. The assignment istentative because the design may not meet speed or timing specificationswith that region assignment. A timing analysis is performed again todetermine whether the low speed region assignment still meets timingspecifications. Note that the timing analysis may be incremental, andmay analyze those parts of the design that experience changed timingbecause of the assignment in order to minimize computation. If the lowspeed assignment violate timing specifications, then the region isre-assigned as a high speed region.

FIG. 11 shows a simplified flow diagram for a method according to anexemplary embodiment of the invention for assigning PLD regions. At 803,all regions are set or assigned as high speed regions. At 806, theuser's design is placed and routed, using CAD software, as describedabove. At 809, timing analysis of the design is performed, and at 812loop counter M is initialized. At 815, the region corresponding to thevalue M is assigned as a low speed region. At 818, timing analysis isperformed, taking into account the assignment at 815. At 821, adetermination is made whether the design meets timing specifications. Ifnot, the region corresponding to the value M is re-assigned as a highspeed region, and the corresponding timing analysis information isrestored to reflect the re-assignment.

At 827, loop counter M is incremented, and at 830 a determination ismade whether all regions have been processed and assigned, or whetheradditional regions remain. If additional regions remain, the loopcontinues and processes those regions.

Many embodiments corresponding to variations of the method describedabove are possible, as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. In oneembodiment, the method sorts the regions after timing analysis andexamines them in order of increasing criticality or decreasing slack. Inthis manner, the method may increase the efficiency of computations andreduce the resources used.

As noted, in another embodiment, one may perform region assignmentsusing a fixed, predetermined speed ratio between the high speed and lowspeed blocks or circuits, e.g., high speed and low speed LABs. Forexample, low speed LABs may be 10% slower than high speed LABs. Thespeed difference between high speed and low speed regions is determinedin advance by analyzing a set of designs and determining the speed ratiothat minimizes power consumption across the set of regions. Acorresponding set of supply and body bias voltages are determined, andcorresponding values are programmed or encoded in NVM 142.

In another embodiment, one may repeat the method described above (andillustrated as the exemplary embodiment of FIG. 11) with differentratios of the speeds of high and low speed regions. The ratios maycorrespond to the different voltage settings encoded in NVM 142, forexample, the speed grades described above. One may then encode in NVM142 the setting that results in minimum power consumption is encoded inCRAM 133 (or vice-versa, as FIGS. 5 and 6 illustrate). Note that some ofthe speed grades may be specified by the user and may be encodeddirectly in CRAM 133 (or NVM 142), as desired.

In another embodiment, one first determines V_(DDL) such that the highspeed regions (e.g., LABs) meet timing specifications. One may do so byusing a worst-case voltage-delay tradeoff curve, giving worst case delayas a function of supply voltage for high speed regions. FIG. 12Acorresponds to this situation, and shows graphs of various delays as afunction of normalized delay, DN. More specifically, FIG. 12A showsgraph 903 of normalized delay of programmable logic, graph 906 ofnormalized delay of programmable interconnect, and graph 912corresponding to the delay model.

The delay data provide the worst case slow down of any resource of thePLD at a given supply voltage compared to a nominal supply voltage,V_(DDN). One may generate the data using either scale factors (e.g.,FIG. 12A), or absolute values, as desired. In other words, the delay ofthe resources may be represented as a ratio compared to their delay atsome nominal voltage, or as absolute delay values across a range ofvoltages. Using this technique ensures that any path through the device,regardless of the types of resources, will be at least as fast as timingspecifications of the critical path dictate (note that at this stage onemay assume that all regions are high speed regions because the HS/LSassignment has not been performed, and HS/LS assignment will not affectthe worst case delay path).

One may then adjust the speeds of the high speed regions and theindividual resource types in the timing model to correspond to thedelays under the chosen V_(DDL). Note that V_(DDL) can be determined byany one of various search algorithms, such as binary search or secantmethod, to determine a voltage at which all resources will fast enoughfor a particular situation. One may then use the method described above(see, for example, FIG. 11) to perform HS/LS region assignment. Notethat in this situation, the method uses the worst case voltage-delaytradeoff during V_(DDL) assignment, and does not take advantage of theparticular mix of resources used in a specific user design.

In another embodiment, the high speed and low speed region assignment isperformed using the assumption that V_(DDL) is the nominal voltage(V_(DDN)). After high speed and low speed region assignment, one mayperform a search to determine the best value for V_(DDL), using exactvoltage/delay scaling for the various resource types and high speed andlow speed circuit blocks (e.g., LABs). The search may constitute any ofa number of well known methods, such as secant or binary search, orother types of search, as persons of ordinary skill in the art who havethe benefit of the description of the invention understand.

At each voltage to be evaluated, a timing analysis is performed. Thelowest voltage that meets timing specifications is then selected andencoded in the parts (e.g., cells or elements) of CRAM 133 thatcorrespond to V_(DDL). Note, however, that in this embodiment, the delayratio between high speed and low speed regions may not be the same atthe chosen V_(DDL) as at the nominal supply voltage, so the choice ofhigh speed and low speed region assignments may not be optimal.

In other embodiments, one may combine the above two approaches. Morespecifically, a first pass estimate of V_(DDL) is performed usingaverage voltage-delay scaling for a typical mix of resource types, asFIG. 12B shows, or an estimate of the resources used by the particulardesign of the user. Note that one may use an average voltage-delayscaling because, if timing specifications are not met, V_(DDL) can befurther refined later. Thus, if this portion of the method produces aV_(DDL) value that does not result in meeting the timing specifications,one may later adjust the value of V_(DDL) so as to meet the timingspecifications (as described below).

Thereafter, one performs high speed and low speed region assignment,using the assumed V_(DDL) value and the associated delay ratio of highand low speed regions and various resource types. In contrast to thefixed delay ratio between low speed and high speed regions (e.g., LABs),the low-speed to high-speed delay ratio will be a function of V_(DDL),but is assumed as a constant once one has chosen a V_(DDL) value. Notethat, at this point, one may determine the critical path for the assumedvalue of V_(DDL) by using a distinct voltage-delay timing model for eachunique resource type. A search is then performed to find the V_(DDL)value that meets timing specifications. This approach performs the highspeed and low speed region assignment using a timing model based on aV_(DDL) value that is close to the final V_(DDL). Thus, it chooses amore optimal value of V_(DDL) and results in a high speed and low speedregion assignment based on that reasonable estimate.

In yet another embodiment, one may iterate the above technique toprovide better accuracy. In other embodiments, the V_(DDL) assignmentmay take place before placement, or after placement but before routing,or at combinations of those points, as desired.

In a simpler embodiment, corresponding to providing a fixed supplyvoltage chosen at the time that the user's design is designed, the CADsoftware simply outputs the desired supply voltage (V_(DDL)). The usermay then use an external source of power that supplies that voltage toPLD 103.

Note that one may apply the inventive concepts effectively to variousICs, including those that include programmable or configurable logiccircuitry, which may be known by other names in the art, as desired, andas persons skilled in the art with the benefit of the description of theinvention understand. Such circuitry include, for example, devices knownas complex programmable logic device (CPLD), programmable gate array(PGA), and field programmable gate array (FPGA).

Referring to the figures, persons of ordinary skill in the art will notethat the various blocks shown may depict mainly the conceptual functionsand signal flow. The actual circuit implementation may or may notcontain separately identifiable hardware for the various functionalblocks and may or may not use the particular circuitry shown. Forexample, one may combine the functionality of various blocks into onecircuit block, as desired. Furthermore, one may realize thefunctionality of a single block in several circuit blocks, as desired.The choice of circuit implementation depends on various factors, such asparticular design and performance specifications for a givenimplementation, as persons of ordinary skill in the art who have thebenefit of the description of the invention understand. Othermodifications and alternative embodiments of the invention in additionto those described here will be apparent to persons of ordinary skill inthe art who have the benefit of the description of the invention.Accordingly, this description teaches those skilled in the art themanner of carrying out the invention and are to be construed asillustrative only.

The forms of the invention shown and described should be taken as thepresently preferred or illustrative embodiments. Persons skilled in theart may make various changes in the shape, size and arrangement of partswithout departing from the scope of the invention described in thisdocument. For example, persons skilled in the art may substituteequivalent elements for the elements illustrated and described here.Moreover, persons skilled in the art who have the benefit of thisdescription of the invention may use certain features of the inventionindependently of the use of other features, without departing from thescope of the invention.

The invention claimed is:
 1. A computer-implemented method of generatinga set of values used to manage power consumption of a programmable logicdevice (PLD), the method comprising: generating, using the computer, aset of points corresponding to process variations of the programmablelogic device; and determining for each point in the set of points, usingthe computer, a set of power supply and/or body bias voltages to beapplied to the programmable logic device at that point, whereinapplication of the set of voltages reduces power consumption of theprogrammable logic device.
 2. The method according to claim 1, furthercomprising generating a model, by using the computer, that provides theset of voltages for each point as a function of a set of measurements oftest circuits in the programmable logic device.
 3. The method accordingto claim 2, wherein the model comprises a linear model.
 4. The methodaccording to claim 2, wherein the model comprises a polynomial model. 5.The method according to claim 2, wherein generating the model comprisesgenerating, by using the computer, a least squares to fit a polynomial.6. The method according to claim 1, further comprising determining, byusing the computer, a correlation of a set of measurements of testcircuits to the set of voltages.
 7. The method according to claim 6,wherein the set of measurements comprises delay measurements.
 8. Themethod according to claim 6, further comprising generating, by using thecomputer, an equation that provides the set of voltages as a function ofthe set of measurements.
 9. A computer-implemented method, comprising:generating, by using the computer, a set of points corresponding to aprocess variation of a programmable logic device (PLD); determining, byusing the computer, characteristics of a test circuit corresponding to apoint in the set of points corresponding to the process variation of theprogrammable logic device (PLD); and determining, by using the computer,optimal supply and/or body bias voltages for the programmable logicdevice (PLD) corresponding to the point in the set of pointscorresponding to the process variation of the programmable logic device(PLD).
 10. The method according to claim 9, wherein determiningcharacteristics of a test circuit corresponding to the point in the setof points corresponding to the process variation of the programmablelogic device (PLD) further comprises simulating, by using the computer,the test circuit.
 11. The method according to claim 9, whereindetermining characteristics of a test circuit corresponding to the pointin the set of points corresponding to the process variation of theprogrammable logic device (PLD) further comprises measuringcharacteristics of the test circuit.
 12. The method according to claim11, wherein measuring characteristics of the test circuit furthercomprises measuring a characteristics of a set of semiconductor dies.13. The method according to claim 9, further comprising generating, byusing the computer, an equation for generating the optimal voltages forthe programmable logic device (PLD).
 14. The method according to claim13, further comprising programming the programmable logic device (PLD)using the generated optimal voltages.
 15. The method according to claim9, further comprising generating, by using the computer, a model forgenerating the optimal voltages for the programmable logic device (PLD).16. The method according to claim 15, further comprising programming theprogrammable logic device (PLD) using the generated optimal voltages.17. The method according to claim 9, further comprising: using thecomputer to select another point in the set of points, determinecharacteristics of a corresponding test circuit, and determinecorresponding optimal voltages for the programmable logic device (PLD).18. The method according to claim 9, wherein determining optimalvoltages for the programmable logic device (PLD) corresponding to thepoint in the set of points corresponding to the process variation of theprogrammable logic device (PLD) further comprises using the computer todetermine the optimal voltages such that a power consumption of theprogrammable logic device (PLD) is reduced or minimized.
 19. The methodaccording to claim 9, wherein determining the optimal voltages such thata power consumption of the programmable logic device (PLD) is reduced orminimized further comprises determining, by using the computer, theoptimal voltages such that a delay specification of the programmablelogic device (PLD) is met.
 20. The method according to claim 9, whereindetermining optimal voltages for the programmable logic device (PLD)corresponding to the point in the set of points corresponding to theprocess variation of the programmable logic device (PLD) furthercomprises using a linear or polynomial model.